1. Field of the Invention
The present invention relates to a control apparatus for electric appliances for domestic use.
2. Description of the Prior Art
Heretofore, the control apparatus for electric appliances for domestic use has been designed so that the setting and control of operating conditions of an electric appliance, such as the switching on or off of a power supply, the degree of volume, the power output level, etc., are effected by rotating or sliding a knob.
There has been a problem in the conventional control apparatus in that it is impossible to prevent the permeation of dust or water drops through an opening formed in a portion of the device through which the shaft of the knob extends and this causes a failure or misoperation of the device. There has been another problem in that the projection of a knob from the body of the device causes the breakage of a shaft of the knob by the application of any unexpected force thereto or an injury to a user.
On the other hand, the use of a membrane type switch panel or a planar switch panel having an elastic film applied onto a surface thereof has been an effective means of overcoming the foregoing deficiencies. However, since each of these planar switch panels is an elastic thin film (generally a resin sheet), it has been impossible to protect a switch portion thereof from the application of a great external force and further there has been a disadvantage that the thin film is damaged by an edge of a knife or metal and an external appearance of the thin film is spoiled or the thin film is ripped open, thereby requiring that such planar switch panels be used with care.
Further, there has been proposed a control apparatus of a touch glass type which has thin films of tin oxide or indium oxide deposited on a glass surface and in which the setting of a user is detected by detecting a hum (an induction noise) or a change in the resistance value between the conductive films caused by a touch of the hand of a user onto one of the conductive films. In this type of control apparatus, while the glass surface acts as an operating surface thereby making it possible to obtain a control apparatus having high reliability as compared with the control apparatus of the previously mentioned types, when the glass surface is rubbed (for a cleaning purpose) with a cleaning agent (e.g., a cleanser) containing polishing powder, minute scratches will still be produced on the glass surface and thereby the thin-film electrode will be cut. Moreover, there is a possibility that the thin film electrode on the touch glass is degraded chemically by an acidic or alkaline cleaning agent although having no physiological effect on the finger of the user, or by cooking juice containing a seasoning matter, etc. when the thin film electrode is used in cooking utensils. Here, it is quite possible that fat or dirt on the user's finger adheres to the glass surface when the user touches the glass surface thereby to set a cooking condition. Also, it is a usual practice to use a cleaning agent as mentioned above to wipe off the extraneous matter from the glass surface. Thus, the touch glass having a thin-film electrode deposited thereon also has a problem from the viewpoint of reliability.